Climate – in fact, ‘cool sunshine’ – is critical to achieving the ripeness and structure necessary for making high-quality Cabernet Sauvignon wines with elegance, latent power and cellaring potential. However, few would describe Stellenbosch’s climate using that term; a more accurate description would be ‘warm’.
How then, does Stellenbosch consistently bottle Cabernet wines of world-class standard? The answer lies in its dramatic – and hallmark – topography, and within that, aspect is critical.
In 1997, RE Schultz defined topography as a static feature of the landscape described by altitude and the rate of change of altitude over distance and therefore including slope form, slope inclination, slope aspect, and altitude or elevation. Today, proximity to oceans, lakes and rivers is included in that definition, as is the relative isolation of hills.
Because of the rapid change in elevation over a relatively short distance – there is just 10 kms between the coastal plain at 5m above sea level to over 1 500m on the Hottentots-Holland Mountains – Stellenbosch’s vineyards have numerous and varying slope aspects. The highest point, Victoria Peak, sits at 1590m above sea level and is a favourite among hikers.
It is these aspects that are critical because of the impact they have on the vineyard’s exposure to winds and ocean breezes, drainage patterns and ventilation as well as the sun’s passage over and penetration into its canopies.
The steeper the slope, the more the aspect will affect its climate, and vineyards which face the sun through much of the day (northerly aspects in the southern hemisphere) are warmer than those which face away (southerly). This not only impacts the ambient temperature in the vineyard itself and within the canopy, it influences soil temperature which in turn affects root growth and function, and, depending on the soil composition, can affect the rate of reflection.
Stellenbosch producers know this, and select their Cabernet sites accordingly; that is, for as much ‘cool sunshine’ they can get.
They can also find relatively cooler sites using elevation. The average elevation in the Stellenbosch district is 136m above sea-level, but the hillside slopes and foothills of its mountains are gentle enough to allow Cabernet vineyards to be planted as high as 350m, and in a few cases to 600m.
As temperature falls (all other things being equal) by 0.6°C for every 100m you climb, this enables those producers with the opportunity to plant on these higher slopes to amplify the benefits of planting on slopes with southerly or south-easterly aspects
Yet another cooling influence would be the vineyard’s proximity to the ocean, its influence extending far inland as sea breezes. It has been pointed out that, at latitude 30°S, South Africa is narrower than South America or Australia and thus the majority of its wine-growing regions are largely under the influence of maritime air.
And, as a result of the prevailing ocean surface and the land/sea ratio, South Africa’s coastal wine region experiences cooler conditions than the latitude might suggest compared to other wine regions at similar latitudes, especially to those in the northern hemisphere.
While Stellenbosch can generally be described as a ‘warm’ grape-growing area, its topography and proximity to the ocean in combination with the seasonal winds (general circulation of the atmosphere), perturbations and ocean currents, create numerous microclimates that deliver the climatic conditions critical for making high-quality Cabernet wines.